Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$138.78	13.388%	$157.3599	$157.36	$157.35	$157.40
Purchase #2	$68.47	4.657%	$71.6586	$71.66	$71.65	$71.70
Purchase #3	$91.80	9.592%	$100.6055	$100.61	$100.60	$100.60
Purchase #4	$59.80	12.802%	$67.4556	$67.46	$67.45	$67.50
Purchase #5	$109.48	13.680%	$124.4569	$124.46	$124.45	$124.50
Purchase #6	$57.86	4.365%	$60.3856	$60.39	$60.40	$60.40
Purchase #7	$176.87	11.851%	$197.8309	$197.83	$197.85	$197.80
7 purchase totals =	$703.06		$779.7530	$779.77	$779.75	$779.90